It is known in the art of broaching to provide for machines which utilize an endless chain for carrying a series of tools into contact with one or more workpieces. Additionally, it is known to utilize machines of this type for producing spur and helical gears. Examples of early machine designs for producing gears with tools carried on articulated links making up an endless chain are disclosed in U.S. Pat. Nos. 1,468,393; 1,469,602; 2,475,690; 2,692,537; and 2,749,804.
Machines utilizing an endless chain for carrying a plurality of tools offer a potential for very high speed production of whatever shape of workpiece is being formed by the tools. In fact, in the case of gear production, it is contemplated that stacks of gear blanks may be worked simultaneously with machinery of this type, rather than one at a time as has been the case with many other types of gear forming (cutting or grinding) machines. However, the requirements for gear manufacture are far more severe than those for other forms of broaching, and therefore, machines of this type have not been, as far as is known, commercially acceptable for high production gear manufacturing needs.
The forming of gear tooth profiles on a work blank requires precise control of an engagement between a workpiece and each stock removing tool, and this requirement demands, in turn, a very rigid machine which maintains precise placement of workpiece and tool under a working load and for a sustained operation of the machine. In machines utilizing endless chains for carrying tools, it is a typical arrangement to provide for a first housing for supporting the endless chain and a second housing for carrying a work spindle which supports one or more work blanks. These two separate housings are mounted on a base in such a way that they can be moved relative to each other to provide for feeding movements of the tools into and out of engagement with different diameters of workpieces. In addition, relative movement may be provided for traversing the workpiece relative to the endless chain and its stock removing tools for generating a series of tooth profiles around the workpiece as it rolls and rotates past the cutting tools.
Provision for relative movement between major housings of a machine tool of this type necessarily reduces the overall rigidity of the machine, and this leads to unwanted deflections between the tools and the workpiece during cutting or grinding operations. Such deflections tend to vary with different stock removal operations and methods, and these deflections are transmitted through the support structures of the machine in the manner of a "spring loop" from the stock removal tools, through the chain support, and back through the work support to the point-of-operation where the tools are engaging the workpiece. In general, the larger the "spring loop," the greater is the loss of precision in maintaining a known relationship between the tools and the workpiece.
It is known to provide for various clamping devices in other forms of gear cutting machinery to control machine rigidity during cutting strokes of a cutter (see, for example, U.S. Pat. Nos. 2,895,385; 3,552,262; and 3,964,369), however it is believed that no similar provision has been made for the type of chain cutting machine contemplated herein. In accordance with the present invention, a very simple clamping means is provided to effectively shorten the spring loop that exists in machinery of the type contemplated, and this, in turn, reduces unwanted deflections between major components of the machine. This is done with a clamping means operative between the housing for the endless chain and the housing for the workpiece, and the clamping means is effective when the stock removing tools of the machine are in engagement with the workpiece. One of the features of the clamping means of the present invention is that it does not interfere with transverse relative movements that are desired between the two major housings which support the stock removing tools and the workpiece, and this is accomplished by mounting a first part of the clamping means on the housing for the endless chain while mounting a second part of the clamping means on a fixed structure of the machine. Thus, the first part of the clamping means is located close to the point at which the cutting forces are transmitted into the chain housing, while the second part of the clamping means is located close to the point where the workpiece is carried. Although this does not constitute a direct link between the housing for the endless chain and the housing for the workpiece (since the workpiece housing must move during a cutting operation), it does provide for an operative clamping of the two major housings since the chain housing is significantly reinforced by its attachment to the fixed structure of the machine and any small remaining deflections of the endless chain housing tend to be followed by the workpiece. In this manner, it is possible to clamp up the machine when it reaches a full depth of stock removal relative to a workpiece even though transverse relative movement between the stock removing tools and the workpiece may be required during the forming operation. Also, the clamping means is operative over a wide range of helix angle positions of the endless chain relative to the workpiece.
In accordance with a specific embodiment of the invention, the clamping means includes a hydraulically operated actuating means for bringing its first and second parts into and out of clamping engagement. The hydraulically operated actuating means includes a piston fitted for reciprocation within a chamber, as carried by fixed structure of the machine, and a hydraulic circuit is provided for delivering a controlled flow of hydraulic fluid to the chamber to cause the piston to move in one direction or another within the chamber.
These and other features of the invention will become apparent in the more detailed discussion which follows, and in that discussion reference will be made to the accompanying drawings as briefly described below.